The present invention pertains to furnaces, and more particularly to a microprocessor control system and method that provides self-correcting features for a furnace.
In most furnaces, when certain operating limits are exceeded, the furnace will shut down requiring immediate maintenance prior to operating again to provide heat. For example, should the combustion air flow provide insufficient or too much combustion air, such that it exceeds a range of acceptable fuel air mixtures, the furnace will shut down. Causes for insufficient combustion air can be vent pipe restrictions, motor failure, or the condensate trap drain overflowing in a condensing furnace. Again, most of the current furnaces will shut down by terminating gas flow and require maintenance prior to operating once again.
Another operating parameter which if exceeded can cause furnace shutdown, is insufficient flow of indoor air to be heated. Insufficient flow of indoor air will result in overheating the heat exchanger assembly, which will activate an over-temperature limit switch that will cause the furnace to shut down. In some furnaces, the furnace may reset itself after the heat exchanger assembly has cooled down, at which time the limit switch will reset. However, if the over-temperature condition continues to exist, the furnace will continually recycle on and off using the same air blower speed.
Causes for insufficient indoor air flow can be a dirty air filter, restrictions in the heating vents, and the like.
In present furnace designs, it is possible that the pilot solenoid gas seat will occasionally not seat properly due to dirt particles or other foreign matter generally from contaminated gas lines. Generally, gas leaks cannot be detected by most of the current gas regulators, thereby presenting an undesirable operating condition in the furnace.